The invention relates to a method and means for producing tubes or pipes with external and, if necessary, internal varying diameters in stages by reducing the tubes over a mandrel by means of grooved rolls having varying diameters, which rolls are mounted in a reciprocating roll stand of a cold pilger rolling mill of the types disclosed in U.S. Pat. Nos. 3,566,658 and 3,890,821.
Tubes or pipes with internally and/or externally thickened portions are required in many commercial and industrial areas. This is especially true for oil field pipes; particularly for drill pipes with thickened ends, which are either formed by hot-rolling or by welding a separate piece on the ends. The required hardness of these ends is achieved by tempering. The financial and technical expense for this process is very great.
It is, therefore, an object of this invention to provide a method and means for substantially reducing the expense involved for producing thickened ends of a pipe by employing a cold pilger rolling mill and the process thereof, wherein the thickened ends are a continuous portion and not disjunct pieces of the produced pipe.
It is well-known to employ in cold pilger mills as to the practice of varying the external diameter of pipes. Two such measures are known: namely, (1) the changing of the roll spacing during the rolling of a pipe; or (2) the changing of the effective length of reduction of a roll groove. The latter measure is achieved by one of two ways: either (a) by changing the effective crank radius so that for the fabrication of an external thickening on the delivery end a part of the length of the groove is not rolled or brought into working contact with the shell, or (b) by rotating the rolls by adjusting the toothed rack upon which the pinions at the ends of the roll shafts are in engagement, so that in this case as well, a part of the length of the groove is not rolled.
Both the above two known measures in the preceding paragraph inherently consists of several disadvantages to the extent they could not efficiently and effectively produce thickened pipe ends. The changing of the roll spacings during the rolling of the pipe requires an expensive mechanical construction of the stand. In both cases, the rolls only form one groove, and the groove width of the rolls coincides to that of the largest pipe diameter and is, consequently, too large for the smaller pipe diameter. This results in poor pipe surface quality and unfavorable deformation properties. This measure or procedure is furthermore unsuitable for the required differences in diameter for drill pipes.
The varying of the effective length of reduction of a roll groove is also disadvantageous. With regard to form (a) i.e. the varying of the effective crank radius, this requires an expensive mechanical construction. In addition to that, no smooth groove is near the vicinity of the thickening portion of the groove so that a poor pipe surface condition is to be expected. For greater differences in diameter, this procedure is unsuitable due to the required widths of the groove resulting in deformation and poor surface quality when the smaller diameter pipe is being rolled. Rotating the rolls by way of form (b) which is by means of adjusting the toothed racks for varying the effective length of reduction represents, indeed, a lesser mechanical expenditure, however, the same disadvantages otherwise occur as for the immediate previously described procedure.
A still further object of the present invention is to provide several grooves around the circumferences of a set of rolls in a pilger mill for fabricating different external diameters, whereby a smoothing zone is associated with each groove and a zone for rotating and/or, advancing the pipe is associated with at least one groove.
While all known cold pilger procedures for the fabrication of varying pipe diameters work solely with one groove, which comes into engagement wholly or partially in the case of external enlargement or thickenings, the invention provides several grooves on one ring roll set, whereby a groove is defined as a closed zone of deformation, which leads from a defined shell cross-section to a defined pipe cross-section.
According to a further object of the subject invention, two grooves are provided, of which a first groove is brought into engagement for the rolling of the large external diameter, and the first and at least a part of a second groove are brought into engagement one after the other for the rolling of the small external diameter of the pipe during a working travel of the stand. This procedure and the configuration of the grooves advantageously provides smoothing zones between the two varying grooves on the ring roll, whereby the quality of the pipe surface and the geometry of the transition zone from a larger to a smaller external diameter is far superior than that of those pipes produced by the previously known procedures.
Another object of the present invention is to provide three grooves, whereby the large external diameter is rolled by a first decreasing groove; subsequently, a first section of the small external diameter is rolled on with an increasing groove, and the small external diameter is rolled out with a further decreasing groove. With this procedure, the length of the transition zone from the large external diameter to the small external diameter can be considerably diminished or tapered while retaining the previously mentioned advantages. In addition, the rotating and advancing of the pipe can take place in the delivery dead center, so that deformation work can be done both during the forward pass or travel of the stand as well as during its backward pass or travel. It is also part of the present invention that the smoothing zone and/or the zone serving for the rotation and/or advancement of the pipe be used in common for two neighboring grooves. This will result in the obtaining of large groove lengths for a given roll diameter.
According to the teachings of the present invention wherein the ring pass roll has two grooves, the first groove runs in a constantly decreasing fashion, whereby the start of this groove is designed to coincide with the diameter of the shell, and the end of this groove is designed to coincide with the large external diameter of the pipe; and the start of the likewise constantly decreasing second groove is designed to coincide with the large external diameter and the end of this groove is designed to coincide with the small external diameter of the pipe, the large and small diameters being of predetermined desired dimensions. By means of this construction of the grooves, a given roll circumference can be used optimally, by virtue of the fact that both grooves can be implemented for the large reduction from the diameter of the shell to the desired final cross-section.
According to the teachings of the present invention the rolls with three grooves, permit the rolling of short transitional areas between the varying diameters, and is characterized by the fact that the ring pass roll is provided with a groove which increases in the direction of rolling, and two additional grooves which decrease in the direction of rolling, whereby the grooves have varying profiles. In this case, the groove which increases in the direction of rolling serves for the substantial rolling out of the pipe, while the grooves which decrease in the direction of rolling serve for the rolling of the thickening portions of the pipe.
According to a further object of the present invention, it is provided that the transition from the engagement of one groove to the next on the workpiece is done by displacing the toothed rack which drives the roll pinion. This measure, is well-known in the art and, in combination with the teachings of the subject invention provides a simple mechanical means to bring into operation the various grooves of the rolls, thereby eliminating or decreasing the costs involved for its installation and operation on already existing cold pilger mills. Furthermore, in the rolling process, it is proposed that for minimizing the shell and mandrel rod forces which occur, the toothed rack is to be constantly oscillated. Preferably, the amount of oscillation of the toothed rack will depend on the rolling program.
For the manufacture of pipes with internally thickened ends, it is proposed according to a particular aspect of the subject invention that the mandrel be provided with a range of varying diameters, which diameters can be made in the pipe by a longitudinal displacement of the mandrel in the zone of deformation of the ring rolls. The mandrel is, as is well-known in the art, divided into a zone for rolling the internal thickening and into another zone for rolling the actual cross-section of the pipe, whereby the various zones are brought into play according to the desired internal diameter. This procedure is well-known, and used in combination with the teachings of the present invention, offers the option of optimally manufacturing pipes having thickened internal diameters and/or external diameter which until the subject invention was only previously economically feasible by means of hot rolling.